1

Abstract— Internal combustion engine for passenger

vehicles are of great concern for transferring heat generated from the combustion inside the engine block. Cooling system of modern day vehicles are compact in design but is responsible to maintain the overall heat transfer at any states of ambient conditions. Heat dissipated through the engine combustion walls is carried out to the radiators by coolant which is liquid cooling. But air cooling at radiator plays a vital role to enhance the efficiency of the coolant heat transfer that is carried out from engine block to the ambient. The study of coolant to ambient (liquid to air heat transfer) in radiator of an internal combustion engine is focused on quest of an optimized configuration of vehicle opening holes and under-hood components as well as the radiator itself to increase the coolant inlet and outlet temperature difference to engine cooling jacket thus improving the cooling system heat transfer at the end. Extensive study of numerical modeling of various types of radiator models and experimental comparisons were reviewed to get a concise idea of economic heat exchanging device for liquid to air heat transfer so far. A wide range of set of design, operating conditions and simulating features of vehicle frontal components for air cooling system were reviewed and evaluated for the efficient cooling purposes. Precision cooling system performance based on frontal air velocity of a vehicle, mathematical models development as well as computational fluid dynamics analysis was studied to identify the research objectives. Keywords: Cooling System, Radiator Heat Transfer, CFD, Passenger Vehicle, Ambient Conditions,

I. INTRODUCTION

Speed, comfort, control, durability, efficiency, etc. these

performances of automotive vehicles are a great concern for this modern era passengers who intend to get the best from it. Various auxiliary components (i.e. turbo-charger, super-charger, etc) are added to improve the efficiency of the engine. Technology for vehicle performance enhancement by providing greater engine power coupled with vogue-driven desires has reduced the size of the engine compartment and the intake areas for internal (underhood)

Md. Hazrat Ali is with Dept. of Mechanical Engineering, Faculty of Engineering; University of Malaya, 50603 Kuala Lumpur, Malaysia (corresponding author to provide phone:+6-0102196210; fax: +603-79674448;email: alihazrat20@yahoo.com).

Masjuki Hj Hassan (email: masjuki@um.edu.my), Md. Abul Kalam (email: kalam@um.edu.my), T.M. Indra Mahlia (email: indra@um.edu.my), Nik Nazri Nik Gazali (email: nik_nazri@um.edu.my), Are with Department of Mechanical Engineering, Faculty of

Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. (Phone: +603-79676863, Fax: +603-79675317)

airflow. These changes tend to add extra heat to the engine cooling system and reduce the volume of air passing through the radiator. The amount of air mass flow depends on the underhood geometry details: positioning and size of the grilles, fan operation, and the positioning of the other underhood components. There is a continuing effort to develop fluid flow simulation capability coupled with heat transfer calculations for the analysis of cooling airflows. It is of course important to get an accurate cooling flow simulation, that the aerodynamics are well modeled.[1]

Figure 1. Liquid-cooled indirect cooling system[2] 1 – Radiator, 2 – Thermostat, 3 – Water pump, 4 – Water passages in cylinder block, 5 – Water passages in cylinder head, The primary function of a typical automotive radiator is to dissipate the unwanted heat carried by the coolant from the engine’s combustion chamber to the surrounding air (ram air and/or fan air), in order to maintain the engine at an optimum operating temperature. The liquid-to-gas cross-flow is the best description of this type of heat exchanger – where air flows in the direction perpendicular to the coolant flow. Because of the difficulty in using any of the known techniques for accurately measuring radiator airflow (and in fact no existing technique can provide fully satisfactory measurement of cooling airflow), the automotive manufacturers have sought alternative methods of inferring aerodynamic performance of cooling systems.[3] This paper is presented as a review of literatures to develop a platform of heat transfer study of available resources about radiator cooling system for passenger vehicles. Numerical

Numerical Model of Heat Transfer Study of Radiators to Enhance

Cooling Performance of Internal Combustion Engine for Passenger Vehicles - A Review.

Md. Hazrat Ali, H. H. Masjuki, M. A. Kalam, T.M.I Mahlia, Nik Nazri

Proceedings of EnCon2010 3rd Engineering Conference on Advancement in Mechanical

and Manufacturing for Sustainable EnvironmentApril 14-16, 2010, Kuching, Sarawak, Malaysia

2

models as well as some experimental results have been redirected from few available sources.

II. LITERATURE REVIEW a. EXISTING SYSTEM OF HEAT TRANSFER CALCULATION FOR

ENGINE COOLING SYSTEM It is well known that air side heat transfer of the radiator is predominantly influenced by the overall heat transfer coefficient of a radiator heat transfer system. The knowledge of cooling air flow and its proper distribution designing may help to determine the effective engine cooling. The compact designing of the modern automotive vehicles and placement optimization of the underhood components beget some constraints for the cooling air flow very difficult. The pressure and temperature fields, less flow velocity of air to radiators, the unknown flow directions of air incoming are also constraints for the radiator air flow quantification. The temperatures of the air and the coolant can be Calculated once the overall heat transfer coefficient, U, is obtained. In order to calculate the overall heat transfer coefficient, the thermal resistance concept is employed in this study.

Figure 2. Equivalent thermal circuit for the heat exchanger core. As illustrated in Fig.2 , the heat is rejected from the coolant to the air through three major thermal resistances: - Convection from the coolant to the inner surface of the tube - Conduction through the tube wall - Convection from the outer surface of the tube to the air via the fins Those thermal resistances are in series as shown in Fig.2.The overall heat transfer coefficient can be defined with these three resistances and the heat transfer rate can be calculated with sub-models for each of the resistances.[4] D. Ganga Charyulu [5] has shown a calculation of how to determine the heat transferred by the radiator to air. There are two parameters commonly found in the literature that are used as efficient ways for evaluating engine cooling performance and optimizing vehicle front-end configurations. These are Air-to-Boil (ATB) and Specific Dissipation (SD). Lin (1999) conducted a detailed investigation into a comparison between ATB and SD, and concluded that SD has significant advantages compared with ATB, particularly when testing in wind tunnels where a chassis dynamometer or climatic control is not available. He concluded that it offers increased productivity for experimental testing compared to ATB.[6] Both parameters can be expressed in terms of the maximum temperature difference across the radiator (Tci – Tai), hence;

And, these equations imply the following relationship;

– Where, Q = heat dissipation rate of the radiator (W) Tci = coolant radiator inlet temperature (°C) Tai = ambient temperature (°C) Tbp = coolant boiling point (°C) This simple relationship is only valid when a value of SD is obtained after the cooling system has established (i.e. when ( Tci – Tai) stays unchanged in time). To establish correlations between these two parameters, further research is needed.

Figure 3. Typical characteristics of Specific Dissipation measured at constant water flows and varying air approach velocities [7] For a given radiator core, a change in SD indicates a change in airflow. It is noted that the relationship is not linear. b. COMPUTATIONAL FLUID DYNAMICS The simple way of measuring the radiator cooling air flow is CFD rather than the experimental techniques as its very expensive as well as time consuming to trial and error procedures, the latest Computational Fluid Dynamics (CFD) techniques seem to offer advantages in resolving cooling problems particularly when used in conjunction with experimental and analytical methods. CFD is a numerical method of solving the partial differential equations that governing the fluid flow, including the continuity equation, the Navier-Stokes equations, the energy equation and/or the k-ε turbulence equations, by converting them into a set of algebraic equations (the process is called discretisation ) to obtain a numerical description of the complete flow field of interest. The elements of CFD generally include numerical algorithm development, transition and turbulence modeling, surface modeling and grid generation, scientific visualization and validation methodologies [8]. Typical discretisation methods used in CFD are finite difference methods, finite volume methods, finite element methods, and boundary element methods.[3]

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III. MATHEM

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MATICAL FORMMODEL REV

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NUMERICAL

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IV. TEST CASE STUDY ACCORDING TO THE MODELING The corresponding baseline geometry which is indicated in Table-1 has been applied for a wide range of experimental conditions, while the baseline working conditions are presented in Table 2. The 5 x 5 air/coolant flow matrix is maintained in each parametric study in order to generate the corresponding performance map (see Fig. 2), from which comparison data between different options can be easily extracted. The numerical tests which have been conducted using an axial grid of 20 CV and a convergence criteria of 1x10-5 to close a pseudo-transient resolution process. The values are obtained from[12] Thermal and fluid dynamic simulation of automotive fin-and-tube heat exchangers. Part 1: Mathematical model.

(a).

(b) Figure 5. Performance maps obtained for a parametric study (fin pitch, Fp, in this case). On the (a), heat transfer dependence on air and coolant flow rates. On the (b), overall enhancement vs. air and coolant flow regimes.

Nomenclature

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Figure 8. Coolant fluid influence on radiator performance. The attention is centered on the highest air flow situation (0.40 kg/s). Fig. 5 depicts the influence of the coolant fluid on both the thermal and fluid-dynamic radiator response. Again , here the notable thing is that the computational tool which was coupled to do the three dimensional studies of the radiator imposes some important restrictions to the available coolant mass flow and acceptable pressure drops of the radiators. The radiator models were studied on various available pass of coolant flow arrangements and of them U configuration (if the coolant flow rate is limited) shows lower coolant pressure drops for highest air flow rate.

Figure 9. coolant lay-out influence on the thermal and fluid dynamic performance of the radiator

V. CONCLUDING REMARKS As per the research point of view I had to go through a lot of literature reviews and of them the very relevant notes are plucked to build up a fresh idea as a whole about the steps to follow for the computational as well as the experimental workings to investigate the radiator heat transfer. The most graphs and the numerical model which been shown here is very updated and depth in workings. Wind tunnel system for the experimental set up of radiator heat transfer may be improved to optimize the conditions being settled with the computational tools. Radiator compact sizing, pressure drop minimization, the front wings simile bumper, opening holes, etc. can be considered in next approach of experimental works maintaining this information from the review as base point.

If CFD simulations can be done successfully within the analytical models then the engine cooling performance of any given vehicle can be predicted without any need of actual hardware or prior to any building of prototype with a distinct feature of acceptance. ACKNOWLEDGEMENT: I would like to express my gratitude to University of Malaya for the accessing of foreign other university dissertations as well as the journal papers.

VI. REFERENCES 1.  Joe  Amodeo,  Ales  Alajbegovic,  and  w.  jansen, 

thermal management simulation for passenger cars - towards total vehicle analysis. 2006. 

2.  Bauer,  H.e.,  Automotive  Handbook.  5th  ed.  ed. 2000: Robert Bosch GmbH. 

3.  Ng,  E.Y.‐T.,  Vehicle  Engine  Cooling  Systems: Assessment  and  Improvement  of  Wind‐Tunnel Based  Evaluation  Methods,  in  Vehicle Aerodynamics  Group,  School  of  Aerospace, Mechanical and Manufacturing Engineering. 2002, RMIT University: Melbourne, Australia. 

4.  Assanis,  D.J.a.D.N.,  Numerical  Modeling  of  Cross Flow Compact Heat Exchanger with Louvered Fins using  Thermal  Resistance  Concept.  SAE  Technical Paper, 2006. 2006‐01‐0726. 

5.  D.  Ganga  Charyulu  a, Gajendra  Singh  b,  and  J.K. Sharmac, Performance evaluation of a radiator in a diesel  engine  ‐  a    Case  study.  Applied  Thermal Engineering, 1999. 19: p. 625‐639. 

6.  Lin,  C.,  Specific  Dissipation  as  a  Technique  for Evaluating  Motor  Car  Radiator  Cooling Performance. 1999, RMIT university. 

7.  Paish,  M.G.  and  W.R.  Stapleford,  A  Rational Approach  to  the Aerodynamics  of  Engine  Cooling System Design. Proc Instn Mech Engrs, 1968‐1969. vol 183: p. 69‐82. 

8.  Hessenius,  K.A.  and  P.F.  Richardson, Computational  Aerodynamics:  The  Next Generation. SAE Technical Paper, 1991( 911988). 

9.  j.  Williams  and  G.Vemaganti,  CFD  quality‐  a calibration study for front‐end cooling airflow. SAE Technical Paper, 1998. 980039. 

10.  K.  Johannessen1,  et  al.,  comparison  between experimental  and  numerical  methods  for evaluating car cooling system design in Melbourne Graduate  Fluids  Conference.  2001:  Monash Uiversity, Melbourne, Australia. 

11.  C. Oliet,  A.O.,  J.  Castro,  and  C.D.  Pe´rez‐Segarra, Parametric  studies  on  automotive  radiators. Applied  Thermal  Engineering  2007.  vol  27:  p. 2033‐2043. 

12.  C.D. Pe´rez‐Segarra, C. Oliet, and A. Oliva, Thermal and  fluid  dynamic  simulation  of  automotive  fin‐and‐tube  heat  exchangers.  Part  1: Mathematical model. Heat Transfer Engineering, May, 2008. vol 29(5): p. 484‐494.